The present invention relates generally to chucks for use with drills or with electric or pneumatic power drivers. More particularly, the present invention relates to a chuck of the keyless type which may be tightened or loosened by hand.
Both hand and electric or pneumatic tool drivers are well known. Although twists drills are the most common tools on such drivers, the tools may also comprise screw drivers, nut drivers, burrs, mounted grinding stones, and other cutting or abrading tools. Since the tool shanks may be of varying diameter or of polygonal cross section, the device is usually provided with a chuck adjustable over a relatively wide range. The chuck may be attached to the driver by a threaded or tapered bore or any other suitable means.
A variety of chuck types have been developed in which a gripping mechanism is actuated by relative rotation between a chuck body and an annular nut. In an oblique jawed chuck, for example, a body member includes three passageways disposed approximately 120.degree. apart from each other. The passageways are configured so that their center lines meet at a point along the chuck axis forward of the chuck body. The gripping mechanism includes three jaws constrained by and movable in the passageways to grip a cylindrical tool shank disposed approximately along the chuck center axis. The nut rotates about the chuck's center and engages threads on the jaws so that rotation of the nut moves the jaws in either direction in the passageways. The body and nut are configured so that rotation of the nut in one direction (the closing direction) with respect to the body forces the jaws into gripping relationship with the tool shank, while rotation in the opposite direction (the opening direction) releases the gripping relationship. Such a chuck may be keyless if it is rotated by hand. One example of such a chuck is disclosed in U.S. Pat. No. 5,125,673 entitled "Non-impact Keyless Chuck," commonly assigned to the present assignee and the entire disclosure of which is incorporated by reference herein. Various configurations of keyless chucks are known in the art and are desirable for a variety of applications.
In chucks where the gripping mechanism includes jaws driven by relative rotation between the nut and the body, the jaws include a threaded portion cut into the generally cylindrical jaws. Referring to the prior art illustration of FIG. 1, threaded portion 10 is cut into a jaw 12, leaving a generally flat surface 14 at the forward edge of the threaded portion. Jaws 12 are disposed in respective passageways 16 and are in threaded engagement with a nut 18 so that rotation of nut 18 drives jaws 12 axially in passageways 16, depending on the rotational direction of the nut. Referring to FIGS. 1 and 1A, when the nut 18 is rotated in the opening direction so that the jaws are driven to their fully retracted position (a position where the tool engaging portions of the jaws are drawn radially outward from the chuck axis a distance greater than the radius of the largest cylindrical tool the chuck is designed to accommodate), flat surfaces 14 axially abut an opposing flat surface 20 of nut 18. Further rotation of nut 18 increases the frictional force between surfaces 14 and 20 until further rotation in the opening direction is inhibited. Frictional forces also resist rotation of the nut in the closing direction, however, and an operator must overcome these forces if the chuck is to be closed to grip a tool.